Multiple explosions hit Brussel, at least 23 people killed

At least 23 people have been killed in three explosions in Brussels, Belgium, according to Belgian media, leaving many injured. Ten were killed at a subway station, according to two Belgian broadcasters, and at least 13 were killed at the airport, according to public broadcaster VRT. The terror threat level in Belgium has been raised to four, its highest level. Two explosions occurred at the city's airport and another blast at a subway station in the suburb of Maalbeek, near the European quarter, where much of the European Union is based. All metro stations in the city have been closed, according to the official Twitter account for the city's transportation agency.
It's unclear what caused the blasts, or if they're related to terrorism.